A known method of reforming gaseous or liquid hydrocarbon fuels is by catalytic steam reforming. In this process, a mixture of steam and the hydrocarbon fuel is exposed to a suitable catalyst at a high temperature. The catalyst used typically contains a nickel oxide deposited on a low silica refractory base and the process usually takes place at a temperature between about 700° C. and about 1000° C. The catalyst is typically placed in tubes in a furnace and the reaction is carried out by passing the gas through the catalyst. Methane or other hydrocarbons react with steam in the reactor tubes to form carbon monoxide (CO), carbon dioxide (CO2), and hydrogen.
In the case of reforming processes for methane or natural gas (the reformation process), hydrogen is liberated in a catalytic steam reforming process according to the following overall reactions:CH4+H2O→CO+3H2 CO+H2O→CO2+H2 While the second reaction is slightly exothermic, the first reaction is highly endothermic and requires an external source of heat and a steam source. The heat required is typically supplied by the combustion of refinery fuel gas, pressure swing adsorber (PSA) purge gas, and/or other fuel gases. Commercial steam reformers typically comprise externally heated, catalyst filled tubes and typically have thermal efficiencies of 60% or less. However, certain stream reformers have higher efficiencies. Exemplary high efficiency reformers are produced and sold by Davy Powergas.
Another conventional method of reforming a gaseous or liquid hydrocarbon fuel is partial oxidation reforming. In partial oxidation reforming, a mixture of the hydrocarbon fuel and an oxygen containing gas are brought together within a partial oxidation chamber and subjected to an elevated temperature, preferably in the presence of a catalyst. The catalyst used is normally a noble metal or nickel and the high temperature is normally between about 700° C. and about 1200° C. for catalyzed reactions, and about 1200° C. to about 1700° C. for non-catalyzed reactions. In the case of methane or natural gas, hydrogen is liberated in a partial oxidation chamber according to the following overall reaction:CH4+½O2→CO+2 H2 This reaction is highly exothermic and once started generates sufficient heat to be self-sustaining. No external heat supply or steam supply is required. The catalytic partial oxidation reforming technique is simpler than the catalytic steam reforming technique, but is not as thermally efficient as catalytic steam reforming.
Another method of reforming a hydrocarbon fuel is autothermal reforming, or “ATR”. An autothermal reformer uses a combination of steam reforming and partial oxidation reforming. Waste heat from the partial oxidation reforming reaction is used to heat the thermally steam reforming reaction. An autothermal reformer may in many cases be more efficient than either a catalytic steam reformer or a catalytic partial oxidation reformer. Using methane, or natural gas, as the hydrocarbon fuel, hydrogen is liberated according to the following overall reaction:CH4+yH2O+(1−y/2)O2→CO2+(2+y)H2, where 0<y<2The end product of the reformation process is typically referred to as synthesis gas. Synthesis gas (syn gas) from the various reforming processes discussed above may be used in a variety of secondary processes. For example, synthesis gases may be used in a processes that combines carbon monoxide and hydrogen to form methanol in the presence of a catalyst.
Of course, it is also well know to use the heat of various processes in an industrial facility to produce steam to generate electricity for other processes within the facility. Exemplary systems that use hot exhaust gases and steam from various industrial processes including the formation of synthesis gas using a steam reformer to produce electricity are disclosed in U.S. Pat. Nos. 6,619,041 and 5,066,325.
Many industrial facilities, particularly in the United States, which have steam reformers for the production of carbon monoxide and hydrogen for use in methanol production, now have relatively inexpensive sources of methanol available. For the operator of many of these industrial facilities, it is more economically attractive to purchase the methanol and other products downstream of steam reformers from a supplier than is to produce the methanol and the like from synthesis gases generated by steam reformers.
As such, a need exists to utilize the exiting steam reformers in a way in which the large capital expenditures associated with these systems may be recouped, while providing a benefit to the facility in which the steam reformer is situated. In these types of facilities, the systems and processes described herein are particularly useful to provide economically attractive alternative uses for stream reformers that represent fixed capital costs for the facility.